This invention relates to the generation of power and has particular relationship to power generators in which the primary source of energy is a nuclear reactor. Nuclear reactor apparatus includes a nuclear reactor in a containment typically in the form of a domed right cylinder of reinforced or precompressed concrete. Inlet and outlet conductors for the primary coolant extend radially at different angles between the reactor and vapor generators. Typically the coolant is pressurized water at about 2250 pounds per square inch pressure and temperature of about 630.degree. F. Other fluids may serve as primary and secondary fluid or only one fluid may be used as in the boiling water reactor and, to the extent that this invention is applicable to such other fluids, reactor apparatus in which such other fluids are used is within the scope of this invention. The vapor steam generators and primary coolant conductors are within the containment and the secondary coolant from the vapor generators is supplied to turbines outside of the containment. Auxiliary components such as pumping equipment and various tanks are contained in other auxiliary buildings outside of the containment.
In accordance with the teachings of the prior art as typified by RESAR 41 the containment and reactor are supported on a flat solid base mat which, depending on seismic conditions, may have a vertical thickness of between nine feet and fifty feet. The containment and mat are herein sometimes called the containment building. The base mat has a slot whose cross section has the form of a key slot and through which the reactor and the core instrumentation tubes extend. In post-tensioned containments just below the mat there is a peripheral chamber which affords access to the stressing tendon anchorages that extend around the containment. A refueling coolant (typically water) storage tank, which is normally used to fill the spent-fuel transfer canal and in the event of a loss of coolant accident is used for emergency coil cooling, is located outside of the containment in prior art apparatus. This tank contains a quantity of coolant which is very large compared to the quantity in the reactor and during a loss-of-coolant accident, this refueling coolant storage tank supplies replacement coolant to the reactor. The supply of this replacement coolant is controlled by valves and electrical switching equipment and is effected by pumping units, each unit typically including a high-head pump, a low-head pump and a spray pump. Each pumping unit and its valves and switching equipment is called a safety injection system train. These pumps as well as the refueling coolant storage tank are connected to the reactor by conductors or piping. The high-head pump operates to supply coolant to the reactor for a small brake in the primary coolant system, the low-head pump for a large break in this system and the spray pump supplies coolant to react with radioactive chemicals (iodine) to wash them into a sump. The coolant from the brake during a loss-of-coolant accident flows into this sump. In the prior-art reactor apparatus the pumping units operate to pump coolant from the refueling coolant storage tank until the tank is empty. Then the pumping units are switched to pump the coolant from the sump into the reactor. This switching is accomplished manually and if the personnel, under the stress of an accident, fails to switch the pumping units timely from the tank to the sump, or the transfer fails for equipment reasons, the reactor loses its coolant supply and may melt. Failure to operate on a test of analogous safeguard pumping units of a boiling water reactor is reported in an article by William Stockton entitled Nuclear Power Plants: How Safe Are They which appeared in the Pittsburgh Post Gazette of Oct. 17, 1974.
The pumping units, valves, and electrical switching equipment constituting the safety injection system are in an auxiliary building outside of the containment. Typically, in the interest of safety, there may be two, three, or four safety injection system trains which in operation inject coolant at angularly spaced positions of the primary coolant system of the reactor. The piping and electrical conductors forming these connections for each train must be isolated from each other. Each train is therefore located on a different floor of the auxiliary building and to enter the containment the piping and conductors of each train are led around the containment periphery to a containment-penetration region. Once inside the containment the piping and electrical conductors fan out or run around an inner perimeter to reach the connecting regions to the reactor. In addition the sump is connected to the trains of pumps, valves and switching equipment through conductors between the inside of the containment and the different floors of the auxiliary building.
Both the auxiliary building containing the above-described safety injection system trains and the containment and its pad are constructed to withstand seismic shocks. However, during a seismic event the building and the containment and pad, being in different locations, may respond differently to shock and the resulting rupture of the interconnections between the containment and the safety injection system trains may materially exacerbate the catastrophe of a seismic disturbance.
The cost of the safety injection system and ancillary structures and components of the prior-art nuclear apparatus is high. A reasonable estimate for these parts of typical prior-art apparatus having two or three safety injection system trains based on 1973 prices is about $20 million; $5 million for the auxiliary building and $15 million for the piping and valves.
It is an object of this invention to overcome the abovedescribed difficulties and disavantages of the prior art and to provide nuclear energy generating apparatus of substantially lower cost than prior-art apparatus in which the structure of the safety injection system shall be simplified and shall operate automatically, and independently of the personnel at a plant, to maintain the flow of coolant through a reactor during a loss-of-coolant accident, and whose damage during a seismic disturbance shall be minimized.
Another object of this invention is to provide a containment and support structure for nuclear energy generating apparatus which shall:
1. Afford structural support superior to that of prior-art apparatus and specific site independence of the containment support structure.
2. Achieve greater economy than prior-art apparatus.
3. Improve the flexibility and afford ready increase of safeguard systems.